Hard disc drives enable users of computer systems to store and retrieve vast amounts of data in a fast and efficient manner. In a typical disc drive, data are magnetically stored on one or more discs which are rotated at a constant high speed and accessed by a rotary actuator assembly having a plurality of read/write heads that fly adjacent the surfaces of the discs.
The heads are suspended from gimbal assemblies extending from arms of the rotary actuator assembly and have aerodynamic features that enable the heads to fly upon an air bearing established by air currents set in motion by the rotation of the discs. Ramp load apparatuses allow a disc drive to spin down when the drive is powered down while preventing the read/write heads from coming into contact with the disc surfaces, while snubber apparatuses serve to protect the discs from deleterious effects that can be caused by the application of mechanical shocks to the disc drive while in its non-operational mode.
Ramp load apparatuses have been utilized that incorporate a stationary set of wedges positioned over the outer edges of the disc surfaces. When a typical drive incorporating this type of ramp load is powered off, a control torque is applied to the actuator arm assembly which rotates the heads toward the outer perimeters of the discs, forcing the gimbal assemblies up onto the ramps of the ramp load apparatus, thereby causing the heads to be lifted away from the disc surfaces. One of the main disadvantages of this ramp load apparatus is that the stationary ramps overlap the outer perimeters of the discs, rendering the disc surface areas below the ramps inaccessible and therefore useless, and thus significantly reducing the amount of disc surface available for data storage.
Another problem with stationary ramp load apparatuses is that the ramps lift up only one side of the gimbal assemblies during the initial stage of engagement. This causes a roll to be induced to the heads, which are still flying in close proximity to the discs. The effect of this induced roll is that one side of the heads is flying closer to the discs than normal, greatly increasing the chance of head to disc interference, which can cause drive failure. Furthermore, stationary ramp load apparatuses rely on the actuator motor to push the heads up onto the ramps. A result of this design is that a force perpendicular to the centerline of the gimbal assembly is applied to the suspension every time a head is loaded onto one of the ramps. This force translates into a rotational moment about the swage joint of the gimbal assembly. The swage joint is a feature that attaches the gimbal assembly to the actuator arm. A rotational moment applied to the swage joint can cause the swage joint to slip during ramp loading, resulting in mis-registration of the heads relative to servo tracks, which can cause either a loss in drive performance or drive failure.
The slope of a stationary ramp affects the amount of disturbance that is induced to the fly height and attitude of a head during loading onto, and unloading from, the ramp. The steeper the slope, the more roll is induced during ramp loading and unloading. The steeper the ramp slope, the faster the head will unload off the ramp and onto the disc, generally causing overshoot and a lower fly height during the transition period as the head settles at its steady state fly height. Conversely, as the slope of a stationary ramp is reduced to minimize these effects, more surface area near the outer perimeter of the discs is lost for data storage.
Of major concern is the potential damage to a disc drive that can occur from a mechanical shock applied to the disc drive. Such a shock can cause the discs and head assemblies to flex, causing physical contact between the discs and the head assemblies. Due to the flexibility of the gimbal assemblies which support the heads, the heads can obtain significant velocities as they accelerate away from and then back into the disc surfaces. Such velocities can be damage both the heads and the disc surfaces.
Furthermore, mechanical shock can impart vibration to the actuator arms, exacerbating the above described flexing and resulting in actuator arm to disc contact. Such actuator arm vibration alone can be of such magnitude as to result in the slider portion of the head assemblies to be lifted from the disc surfaces. Not only can these vibrations from shock cause damage to the discs and head assemblies, they can result in deleterious debris generation which can lead to total drive failure.
Stationary disc snubbers have been used to limit the deflection of the discs of a disc drive from resulting from mechanical shock. The function of such a disc snubber is to prevent damaging contact of the discs and the actuator arms/head assemblies. Since the discs are rotating at high rotational speeds during the operation of the disc drive, disc contact during operation of the disc drive with a stationary snubber can cause major disc damage and particle generation. Thus, high operational shock requirements can preclude the use of such snubbers.
Not only is there a need to protect the disc drive during the time that the disc drive is powered off, there is a need for disc snubbing to protect non-operating discs from the effects of mechanical shocks without incurring potential contact with the discs during operation.